The global effects of stroke on the human electroencephalogram

The scaling properties of the fluctuations of EEG time series are used in an investigation of acute stroke in humans. We use detrended fluctuation analysis to characterize the fluctuations in 10-second time series in terms of two dimensionless scaling exponents. The statistics of these scaling exponents across 129 scalp sites define measures which may be used to distinguish normal subjects from those with acute cerebral ischemia. By their nature, these statistics emphasize the global properties of EEG dynamics. Simulation of a focal anomaly which accurately reproduces the mean scaling exponents for stroke subjects contradicts the data for the variances, which we take as evidence that the effect of stroke on EEG is global.